1. Field of the Invention
The present invention relates to a self cooling table top centrifuge and, more particularly, to a method and apparatus for providing refrigeration capabilities to a table top centrifuge at a lower price and complexity level than available heretofore.
2. Description of the Prior Art
Small, table top centrifuges are used in a clinical lab primarily to separate solid particles such as blood cells and the like from physiological fluids for further processing of either the sediment or the fluid for further processing of either the sediment or the fluid for diagnostic purposes. A typical table top centrifuge includes a rotor positioned within a chamber in a housing, the housing having a cover to enclose the chamber during operation of the rotor. In the case of high speed centrifuges, the chamber is typically evacuated so that the rotor operates in a vacuum. On the other hand, vacuum chambers are not ordinarily used with low speed, table top centrifuges.
Due to the nature of the centrifuging process, i.e. the rotor spinning in an air environment and the resultant friction between the rotor surfaces and the air, the rotor and the sample therein tend to heat up. In many centrifuges, ports are provided to circulate room air through the chamber to limit the temperature rise to a minimum. Even so, within a short period of time, the sample temperature will rise by as much as 10.degree. centigrade over the prevailing room ambient. Quite often, the resuling elevated temperatures may be detrimental to the sample by causing deterioration and/or side reactions affecting further diagnostic tests.
To prevent such occurrences, samples suspected of being temperature sensitive have required much costlier refrigerated floor model centrifuges. In a typical prior art refrigerated centrifuge, the evaporator coils are wrapped directly around the chamber walls to directly cool the walls of the chamber so as to cool the air and the rotor therein through the combined effects of conduction and radiation. However, this causes condensation and frost formation within the chamber and problems such as corrosion, contamination, and curtailed run times due to physical blockage by icing conditions. This latter problem is primarily the result of the necessity of maintaining the chamber walls well below freezing temperatures due to the limited surface area and thus the poor heat transfer conditions available.